Small rat islets are superior to large islets in in vitro function and in transplantation outcomes

Abstract

Barriers to the use of islet transplantation as a practical treatment for diabetes include the limited number of available donor pancreata. This project was designed to determine whether the size of the islet could influence the success rate of islet transplantations in rats. Islets from adult rats were divided into two groups containing small (diameter Ͻ125 m) or large (diameter Ͼ150 m) islets. An average pancreas yielded three times more small islets than large. Smaller islets were ϳ20% more viable, with large islets containing a scattered pattern of necrotic and apoptotic cells or central core cell death. Small islets in culture consumed twice as much oxygen as large islets when normalized for the same islet equivalents. In static incubation, small islets released three times more insulin under basal conditions than did large islets. During exposure to high glucose conditions, the small islets released four times more insulin than the same islet equivalencies of large islets, and five times more insulin was released by the small islets in response to glucose and depolarization with K ϩ . Most importantly, the small islets were far superior to large islets when transplanted into diabetic animals. When marginal islet equivalencies were used for renal subcapsular transplantation, large islets failed to produce euglycemia in any recipient rats, whereas small islets were successful 80% of the time. The results indicate that small islets are superior to large islets in in vitro testing and for transplantation into the kidney capsule of diabetic rats. islet transplant; insulin secretion; viability THE RISE IN CASES OF DIABETES MELLITUS in the United States has been called an epidemic. It is the third leading cause of death by disease and rivals heart disease and cancer as a major killer of United States citizens. For unexplained reasons the occurrence of type 1 diabetes is increasing worldwide, and the age of onset has decreased by 3-5 yr over the past decade so that many children now develop diabetes before entering school. The result is that more people with diabetes will spend a larger percentage of their life at risk for developing the chronic complications related to type 1 diabetes. Because the risk for development of most of the chronic complications associated with diabetes is related to glycemic control, significant attention is directed toward novel therapies, such as islet transplantation, to improve glycemic control.Islet transplants in humans were first attempted in the 1980s (7, 8). Initial success rates for human islet transplantation were disappointing, with only 5% of patients receiving transplants achieving partial function (19). Amid the failures were isolated success stories of individuals achieving prolonged reversal of their diabetes for a 1-to 2-yr period (19), which encouraged researchers to continue this approach for the treatment of diabetes. In 2000, islet transplantations were performed successfully on seven patients with diabetes by using a suppression regimen that omitted glucocorticoid...

Reduction of diffusion barriers in isolated rat islets improves survival, but not insulin secretion or transplantation outcome

“…The observation of core cell death within large islets was shown previously to occur in islets over 200 µm in diameter. 8,9 In published reports, 5,6 we found signs of core cell death in even smaller islets of 150 µm in diameter, but until now had not quantified the degree of dead islets. We defined core death as a region in the center of the islet where >50% of the cells were dead, which is a more stringent criteria than used by other laboratories.…”

“…5 Our previous work demonstrated that large isolated islets have poor oxygen utilization, poor survivability following isolation, and secrete less insulin than small islets when normalized for the same volume. 5,6 When diabetic rats were transplanted with a marginal mass of large islets, none of them became insulin independent. In contrast, when an equivalent mass of small islets was transplanted into diabetic rats, 80% became insulin independent and remained that way for the 2 month duration of the experiment.…”

Filtration is a time-efficient option to Histopaque, providing good-quality islets in mouse islet isolation

“…Some articles have reported the superiority of rodent and human islets under 100-125 lm against large islets in in vitro and in vivo function (MacGregor et al 2006;Lehman et al 2007;Farhat et al 2013). In this regard, Fujita et al (2011) reported that large islets secreted less insulin than small islets per islet equivalent.…”

Inhibition of Gamma-Secretase Activity Promotes Differentiation of Embryonic Pancreatic Precursor Cells into Functional Islet-like Clusters in Poly(Ethylene Glycol) Hydrogel Culture

“…17 After significantly increasing in size from day 0 to 7, differentiated islet-like clusters on day 14 are all below 125 mm in diameter, a cutoff above which mature isolated rat islets have lower in vitro viability and stimulated insulin release, as well as a diminished in vivo efficacy. 42 Among necessary nutrients for cell growth, oxygen availability is typically limiting due to its low solubility in the absence of a carrier protein such as hemoglobin, 43 and studies indicate that the maximum size of islets that maintain sufficient oxygen diffusion ranges from 100 to 150 mm. 44,45 Our data demonstrate that encapsulated cell clusters transition through a period of proliferation and increasing cluster size; however, once differentiation commences, differentiating islet-like clusters selfregulate to a size conducive for sufficient oxygen diffusion throughout the aggregate.…”